Adhesive sheet material



Patented July 10, 1945 ADHESIVE SHEET MATERIAL Edward Sidney Hole, London E. C. 4, England No Drawing. Application April 11, 1942, Serial No. 438,659. In Great Britain May 13, 1941 2 Claims.

This invention relates to adhesive impregnated sheet materials, and more particularly adhesives in or for use with a carrier and intended to have a quick drying and very adhesive character suitable for work where the maximum tenacity and flexibility is required, e. grfor applying printing plates both metallic and plastic to wood or metal bases or to curved cylinders and many other industrial purposes, and also for domestic and like purposes. In connection with the adhesion of printing plates to bases and cylinders, previous compounds in use often become too brittle with the result that the plate was liable to fly from its base or cylinder, or the compounds are not sufficiently tenacious especially at the corners or edges of the plates, or still further they involve an undesirably protracted period in setting, whilst the low melting point of some of the compounds is an objection to their practical use under conditions where heat is generated as in printing and analogous machinery. The use of a permanently tacky adhering medium such as the existing tacky rubber coated linen or like strips is also unsuitable because such material is not easy to handle cleanly and it cannot be mailed or stored for use without protecting the adhesive surfaces with a' layer of gauze, tissue paper or other removable protective coatin and also because its normal condition is tacky it will not set or harden readily. In the mountin of. printing plates, more particularly plastic plates of the thermo-setting or thermofast moulded type, it is desirable to use a flexible highly tenacious adhesive which will set and harden rapidly Without however using excessive heat and pressure liable to injure the plates. The chief object of this invention is to achieve this desideratum in such manner that although the adhering medium is potentially adhesive it can be prepared ready for use, preferably in a fabric or other thin sheet carrier so as to provide a substantially dry non-tacky sheet which is only rendered tacky during its actual use for mounting a printing plate or for an analogous purpose. Such a sheet may be handled, packed, stored or transported without any special surface covering.

In one form of the invention in which a fabric or paper sheet carrier is employed in the provision of a normally dry medium for adhering a printing plate to a base or cylinder, the adhering medium comprises intimately amalgamated gutta percha, a thermoplastic, tack-producing substance known in the art as an adhesive agent such as e. g. wood pitch or a resinous substance,

and tenacity such as petroleum jelly or a metallic soap. Such a medium can be handled, packed, stored and transported without any protective surface covering.

If the adhesive medium is to be produced without a fabric carrier and in solid or liquid form it should be made with a bigger proportion of flexible component and a lesser proportion of adhesive component which is explained by the fact that the fabric itself imparts a flexibility to the whole, while the adhesive pure and simple must supply itspwn flexibility.

The foregoing refers to the development of a potential but latent adhesiveness brought out by means of heat. When handling the adhesive in a melted state its extreme tenacity can be counteracted if the surface upon which it is poured for cooling off into solid form is previously brushed or wiped with a solution of glycerine and magnesium hydrofluosilicate in water. This solution is useful in all cases where it is desired to handle the solid, liquid or fabric form in a tacky or semi-tacky state.

For normal requirements, e. g. for use in nontropical climates or normal temperature stores and works I have found that good results are obtained if gutta percha is compounded with thermoplastic tack-producing agents. In this manner rosin (colophony) various resins or resenes (including some of the so-called gums) as also various kinds of so-called pitch and the like with or without a constituent to enhance flexibility and prolong tenacity such as a little petroleum jelly or a metallic soap (zinc oleate for instance) or similar agent, can be combined by heat with the gutta percha in such a manner that each constituent shares its characteristic with the other and the desired flexibility can be obtained if the gutta percha preponderates while the accompanying adhesive material is such that it can give sufiicient tenacity though in comparatively small proportion to the total bulk. The gutta percha gives the flexibility and the pitch or resin the adhesion, the former counteracting the brittleness of the latter. By this means a composition of matter forming a highly tenacious adhesive, which can be used in or separate from a carrier, comprises intimately amalgamated gutta percha, an adhesive or potentially adhesive material, and an auxiliary flexibility or tenacity enhancing agent.

When the carrier is a fabric a cheap product can be obtained by first impregnating the fabric with a weak solution of latex and afterwards apand if desired a plasticizer to enhance flexibility u plying the gutta percha compound which consequently is thus spread about entirely on the surface and spread over a wider area for a given quantity than would be possible without this preliminary impregnation with latex.

The amalgamation can be effected by prolonged heating, the gutta percha being melted with rosin, resin or resene (including some of the so-called gums) or other suitable potentially adhesive material such as wood, pitch or the like, or other adhesive substances, or with a combination of such materials or substances. It is found that if the heating is prolonged to ensure complete melting of the ingredients so that the ingredients intimately amalgamate that the resultant product is a firm body which can be spread by heat over one or both of the surfaces to be united and in which the flexibility and tenacity of the gutta percha will co-operate with th adhesive action of the remaining ingredient or ingredients to enable the appropriate surfaces to be pressed together and for adherence to take place immediately the substance cools. The'product can also be used with a suitable solvent, and the adhesive can be brushed or sprayed on the required surfaces to be adhered together, and after volatilisation of the solvent one or both of the coated surfaces can be warmed to render the substance tacky and the two surfaces pressed together when complete adhesion will take place. This latter method is particularly efiicacious when flexible curved plates,, such as printing plates, are to be attached to a cylinder. By way of example a suitable manner of manufacturing the adhesive is to heat in a suitable pan colophony or wood pitch and gutta percha until a homogeneous'liquid is obtained free from large surface bubbles. The proportions of ingredients, which can be varied according to the contemplated use or character of the finished product, can comprise four parts by weight of wood pitch, and six parts by weight of gutta percha, and the addition of about one part of petroleum jelly or zinc oleate. If desired there may be two parts of each of colophony and Swedish pitch instead of four parts of Swedish pitch, and the gutta percha is cut into small pieces to accelerate the action. To raise the melting point adhesive agents of high melting point, such as mastic dammar or the like can be used in addition to (or in substitution for part of) the wood pitch or colophony. Also the addition of some metallic soaps such as calcium or magnesium stearate achieve this higher melting point and the product hardens more rapidly. They also reduce or abolish the tendency to slide sideways which the adhesive otherwise shows before it is completely hardened. The amount of such soap used can be determined according to the particular use of the adhesive but for all ordinary purposes about ten percent of the total weight is a suitable proportion. For some purposes three or even four parts by weight of the gutta percha can be present with only one part of rosin or one part of pitch, more particularly when intended for use without th fabric carrier. This high proportion of gutta percha makes the product more expensive but greatly increases the flexibility, tenacity and dependability of the compound when used without fabric as a direct adhesive.

If a suitable fabric is impregnated with the compound as described above and allowed to dry then pieces of it can be made to adhere to the back of a printing plate by heat and a little pressure applied for quite a short period. Such plate with its fabric backing can be sent through the post without any protective gauze and the recipient has only to warm the plate when it can immediately be fastened to the mount by means of the adhering impregnated fabric. It is, of course quite clear that if plates are coated thickly with the adhesive in liquid form and if suitable gauze or fabric be then pressed upon them, enough of the liquid may exude through the mesh of the material to render the back tacky and, if allowed to set, such plates can be sent to any recipient for fastening to mounts by heat.

Reference is uniformly made herein to the impregnation of a suitable fabric. This is because experience has shown that when paper is used it has a tendency to split itself into two sheets and the block is liable to fly from the mount. This happens even with tissue paper. In the case of rubber plates, however, which are usually printed from rapidly rotating cylinders, it is customary to afiix them to sheets of kraft paper which are in turn easily fixed into position on the cylinder and are cut to suitable sizes for this purpose. Thus you may print a rubber plate which is only 3 inches square amxed to the middle of a sheet of kraft paper which is afoot square. To meet such cases I have coated the whole of one surface of sheets or rolls of kraft paper with one or other of my compounds. To fix the rubber plate it is warmed and pressed into position in the case of the gutta percha compound. In this case it is necessary to press the plate upon the coated paper and this can be done by a roller in the case of half tone plates but in the case of text or line work where there are large sunken whites on the plate it is obvious that a roller would not transmit any pressure to these sunken portions. This difficulty is overcome by the expedient of hitting the face of the plate with an ordinary stereotypers brush.

I claim:

1. An adhesive sheet material comprising a layer of fabric coated on both sides with a normally dry, flexible, non-tacky, heat-activatable adhesive comprising a major proportion of gutta percha and a minor proportion of a mixture of wood pitch and petroleum jelly.

2. An adhesive sheet material comprising a layer of fibrous material coated on both sides with a normally dry, flexible, non-tacky, heat-activatable adhesive comprising a major proportion of gutta percha and a minor proportion of a mixture of an adhesive agent selected from the group consisting of rosin, natural gum and wood pitch and a plasticizer selected from the group consisting of petroleum jelly and an insoluble metallic soap.

EDWARD SIDNEY HOLE. 

